Electrostatic or xerographic printers and copiers essentially operate in different stages including charging, exposure, developing, transferring, and fusing, as is well known. During the charging stage, a charge receptor or photoreceptor, typically in the form of a belt or cylindrical drum, is electrostatically charged with a high voltage wire, which is referred to as a corona wire, or a charge roller. The drum includes a coating of photoconductive material, which includes a semiconductor that becomes conductive when exposed to light. In many architectures there are provided multiple photoreceptor drums, one for each primary color used in the printing process. In other architectures, a single photoreceptor is charged, exposed, and developed at multiple stations, one for each primary color used in the printing process.
In order to generate an adequate amount of corona to initially charge the photoreceptor (hereinafter described as a cylindrical drum), each of the electrodes associated with solid state charge devices (SSCD), which are used to charge the cylindrical drum, is preferably energized. An aperture associated with the SSCD should also be in good condition and present low impedance to electrode current flowing thereto in order to generate a satisfactory corona. Issues with connections between a power supply associated with the copier and the SSCD or within the power supply often preclude an adequate corona. However, if these issues are detected, prints with reduced image quality may be reduced or eliminated. Monitoring the electrode current to the SSCD with a current sense resistor is one method for detecting these issues. However, due to the high frequency of the electrode current (such as about 100 kHz), such a detection circuit requires an amplifier with a relatively high slew rate, which adds significant cost and unreliability.
Accordingly, it would be desirable to provide a method and apparatus for effectively and efficiently monitoring the condition of SSCDs associated with electrostatic printers that overcome disadvantages of the prior art to permit high-quality copier output.